A battle of the Open Cup specialists of the MLS era looms in the semi-finals of this year's competition, as the Chicago Fire and Seattle Sounders won their quarter-finals and Philadelphia Union survived some extreme weather to book a trip to FC Dallas.Dallas negotiated a trip to face the NASL's Carolina Railhawks, who had beaten a full-strength LA Galaxy in the previous round and Chivas USA before that.

It's one of the quirks of the Open Cup's broadly regional organisation in the early rounds that the Railhawks often find themselves hosting, and beating, western MLS opposition. Before the Galaxy defeat, Landon Donovan had complained of his team being "sick" of traveling across country to be beaten by the North Carolina team.If there was doubt about the outcome in Dallas minds it didn't show, even when the Railhawks took a ninth-minute lead through Zach Schilawski. Two late goals might have put a gloss on the 5-2 scoreline but in truth, after Fabian Castillo's 44th-minute goal to make it 3-2, Dallas never looked in trouble.Dallas will now host the Union, whose Open Cup goalscoring specialist Sebastien Le Toux broke the modern-era tournament record in a 2-0 victory over New England. It took a while – a violent dust storm accompanied by thunder and lightning saw the game halted for an hour in the 61st minute, before Philadelphia, 2012 semi-finalists, saw the game out.The other NASL team left in the quarter-finals, the Atlanta Silverbacks, gave Chicago a scare in the first half, with the Fire grateful for goalkeeper Sean Johnson. Indeed it was only when Atlanta tired late on that Chicago were able to pull away, thanks to a Jeff Larentowicz penalty and a goal from Alex in the final 10 minutes.The Fire are one of the MLS teams who consistently emphasise the importance of an Open Cup they won as part of a double in their first year of MLS play, back in 1998. They will meet like minds in Seattle, whose three-year winning streak was ended by Sporting Kansas City in 2012. The Sounders fell early last year, but have been determined to recapture the Open Cup, and beat rivals the Portland Timbers last night in front of rather fewer fans than the 67,000 expected for Sunday's televised league game.In a tight match that was forced into extra time by Darlington Nagbe's injury time leveller after Ossie Alonso's second-half goal, the difference was an extra-time red card to Diego Chara. Goals from Kenny Cooper and Marco Pappa eased the Sounders through to host Chicago.